U.S. patent number 6,493,619 [Application Number 09/930,168] was granted by the patent office on 2002-12-10 for lane keeping assistance system and method for automotive vehicle.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Hiroshi Kawazoe, On Sadano, Shigeki Sato, Masayasu Shimakage.
United States Patent |
6,493,619 |
Kawazoe , et al. |
December 10, 2002 |
Lane keeping assistance system and method for automotive
vehicle
Abstract
In lane keeping assistance system and method for an automotive
vehicle, a control current (Iout) to be outputted to a motor during
an automatic steering mode is detected, a filter is provided for
the detected control current to pass only signal components of the
detected control current whose frequencies are lower than a
predetermined cut-off frequency value (fstr, fstr_low, fstr_mid,
fstr_hi) to derive a filtered control current (Iout_lpf), a
determination of whether a manual steering intervention to the
automatic steering occurs is made according to a magnitude of the
filtered control current, and the control current outputted to the
motor is reduced toward zero when the manual steering intervention
is determined to occur according to a result of determination that
the magnitude of the filtered control current (Iout_lpf) is in
excess of a predetermined threshold current value
(Iout_lpf_th).
Inventors: |
Kawazoe; Hiroshi (Kanagawa,
JP), Shimakage; Masayasu (Kanagawa, JP),
Sadano; On (Kanagawa, JP), Sato; Shigeki
(Kanagawa, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
18755024 |
Appl.
No.: |
09/930,168 |
Filed: |
August 16, 2001 |
Foreign Application Priority Data
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Sep 5, 2000 [JP] |
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2000-268218 |
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Current U.S.
Class: |
701/41; 180/168;
340/435; 701/117; 701/118; 701/28; 701/514; 701/96 |
Current CPC
Class: |
B62D
1/286 (20130101); B62D 5/0463 (20130101); B62D
15/025 (20130101); B60T 2201/08 (20130101); B60T
2201/087 (20130101) |
Current International
Class: |
B62D
5/04 (20060101); B62D 15/00 (20060101); B62D
1/28 (20060101); B62D 15/02 (20060101); B62D
1/00 (20060101); G06F 165/00 (); G05D 001/00 () |
Field of
Search: |
;701/41,28,42,117,118,207,211,220,223,225,301,96 ;180/168,169
;340/435,436 ;342/456 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 640 903 |
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Mar 1995 |
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EP |
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9-240502 |
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Sep 1997 |
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JP |
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Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Donnelly; Arthur D.
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A lane keeping assistance system for an automotive vehicle,
comprising: a traffic lane information detector to detect an
information related to a traffic lane on which the vehicle is about
to run; a steering angle sensor to detect a steering angle of a
steering wheel of the vehicle; a steering position changing section
by which the steering wheel of the vehicle is enabled to be
displaced independently of a manual steering operation through the
steering wheel; a controlled steering target value setting section
that sets a controlled steering target value when a controlled
steering to follow the traffic lane is carried out on the basis of
at least the traffic lane related information detected by the
traffic lane information detector and the steering angle detected
by the steering angle sensor; a controlled steering command value
setting section that outputs a control command value in accordance
with the controlled steering target value; a control command value
filtering section that filters the control command value to pass
only frequency components of the control command value lower than a
predetermined filter threshold value to derive a filtered control
command value during an execution of the controlled steering; a
manual steering intervention detector to detect a steering
intervention state to the controlled steering by the manual
steering operation when the filtered control command value is in
excess of a predetermined threshold control command value; and a
controlled steering target value limiter to reduce the control
command value toward zero value to suppress the controlled steering
target value toward a lower value direction including zero when the
manual steering intervention is detected by the manual steering
intervention detector.
2. A lane k ee ping assistance system for an automotive vehicle as
claimed in claim 1, further comprising: a vehicular velocity
detector to detect a vehicular velocity of the vehicle; and a
predetermined threshold value varying section that varies the
predetermined filter threshold value when the control command value
filtering section provides the filter for the control command value
to pass only predetermined frequency components lower than the
predetermined filter threshold value, and wherein the predetermined
threshold value varying section varies the predetermined threshold
value of the filter thereof toward a higher frequency side as the
detected vehicular velocity becomes increased.
3. A lane keeping assistance system for an automotive vehicle as
claimed in claim 1, further comprising a lateral displacement
detector to detect a lateral displacement of t he vehicle from a
center position of the traffic lane on the basis of the traffic
lane information from the traffic lane information detector and
wherein the manual steering intervention detector detects the
steering intervention state by the manual steering operation w hen
the filtered control command value is in excess of the
predetermined threshold control command value and the detected
lateral displacement is in excess of an external disturbance
determination threshold value.
4. A lane keeping assistance system for an automotive vehicle as
claimed in claim 1, wherein the steering position changing section
comprises an electric motor and the control command value is a
current to be supplied to the electric motor.
5. A lane keeping assistance system for an automotive vehicle as
claimed in claim 1, wherein the filter of the control command value
filtering section comprises a low-pass filter and the predetermined
filter threshold value is a cut-off frequency of the low-pass
filter.
6. A method applicable to a lane keeping assistance system for an
automotive vehicle in which a control current is outputted to a
motor of an automatic steering actuator coupled to a vehicular
steering system to provide a steering force thereto to follow the
vehicle along a traffic lane on a road located in a vehicular
forwarding direction during a vehicular run in an automatic
steering mode, the method comprising: detecting the control current
to be outputted to the motor during the automatic steering mode;
providing a filter for the detected control current to pass only
signal components of the detected control current whose frequencies
are lower than a predetermined threshold frequency value of the
filter to derive a filtered control current; determining whether a
manual steering intervention to the automatic steering occurs
according to a magnitude of the filtered control current, the
manual steering intervention being determined to occur depending on
whether the magnitude of the filtered control current is in excess
of a predetermined threshold current value of the filter; and
reducing the control current outputted to the motor toward zero
value when, at the manual steering intervention determining step,
the manual steering intervention is determined to occur according
to a result of determination that the magnitude of the filtered
control current is in excess of the predetermined threshold current
value.
7. A method applicable to a lane keeping assistance system for an
automotive vehicle as claimed in claim 6, further comprising
detecting a vehicular velocity and wherein the predetermined
threshold frequency value is a cut-off frequency of the filter, the
cut-off frequency being varied toward a higher frequency side as
the detected vehicular velocity becomes higher.
8. A method applicable to a lane keeping assistance system for an
automotive vehicle as claimed in claim 6, further comprising:
detecting a vehicular velocity, wherein the filter comprises a low
vehicular velocity low-pass filter having a lowest cut-off
frequency (fstr_low), a middle vehicular velocity low-pass filter
having a second lowest cut-off frequency (fstr_mid) , and a high
vehicular velocity low-pass filter having a highest vehicular
velocity cut-off frequency (fstr_hi), and wherein, at the filter
providing step, one of the low-pass filters is selected according
to a magnitude of the detected vehicular velocity and the filtered
control current is calculated.
9. A method applicable to a lane keeping assistance system for an
automotive vehicle as claimed in the claim 8, further comprising
detecting a traffic lane related information and detecting a
lateral deviation of a vehicular position from a center position of
the traffic lane on the basis of the detected traffic lane related
information and wherein, at the manual steering intervention
determining step, the manual steering intervention is determined to
occur when the filtered control current is in excess of the
predetermined threshold current value and when the detected lateral
deviation is in excess of an external disturbance determination
threshold value.
10. A method applicable to a lane keeping assistance system for an
automotive vehicle as claimed in claim 9, wherein, at the control
current reducing step, the control current is gradually reduced
toward zero value.
11. A lane keeping assistance system for an automotive vehicle,
comprising: traffic lane information detecting means for detecting
an information related to a traffic lane on which the vehicle is
about to run; steering angle detecting means for detecting a
steering angle of a steering wheel of the vehicle; steering
position changing means by which the steering wheel of the vehicle
is enabled to be displaced independently of a manual steering
operation through the steering wheel; controlled steering target
value setting means for setting a controlled steering target value
when a controlled steering to follow the traffic lane is carried
out on the basis of at least the traffic lane related information
detected by the traffic lane information detecting means and the
steering angle detected by the steering angle detecting means;
controlled steering command value setting means for outputting a
control command value in accordance with the controlled steering
target value; control command value filtering means for filtering
the control command value to pass only frequency components of the
control command value lower than a predetermined filter threshold
value to derive a filtered control command value during an
execution of the controlled steering; manual steering intervention
detecting means for detecting a steering intervention state to the
controlled steering by the manual steering operation when the
filtered control command value is in excess of a predetermined
threshold control command value; and controlled steering target
value limiting means for reducing the control command value toward
zero value to suppress the controlled steering target value toward
a lower value direction including zero when the manual steering
intervention is detected by the manual steering intervention
detecting means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to lane keeping assistance
system (also called, a lane following vehicle control system, but,
hereinafter, is referred to the lane keeping assistance system) and
method for an automotive vehicle. The present invention relates
more particularly to a technical field of the lane keeping
assistance system and method in which an automatic steering is
carried out in such a way that a traffic lane information is
retrieved during a vehicular run and a steering torque is given to
a steering force transmission system to follow the vehicle along a
traffic lane at a forward direction of the vehicle or a driver's
steering operation is supported to follow the traffic lane at the
vehicular forward direction by providing a steering reaction torque
is given to a vehicular steering force transmission system.
2. Description of the Related Art
In general, the lane keeping assistance system has a region in
which the vehicle can autonomously run along a white line and in
which a development force by an actuator does not give an influence
on a steering intervention. Hence, it is necessary to reduce the
development force by a control quickly if a driver's steering
intervention occurs.
On the other hand, in a system in which a gear direct drive power
steering is used, a torque sensor mounted on a column shift of a
steering wheel can directly be used to determine the driver's
steering intervention.
A Japanese Patent Application Publication No. Heisei 9-240502
published on Sep. 16, 1997 exemplifies a previously proposed lane
keeping assistance system.
In the above-described Japanese Patent Application Publication, a
torque sensor is installed to detect a steering torque from a
vehicular driver in order to switch between an automatic steering
and a manual steering by an accurate trap of an intention of the
vehicular driver. When an output of the torque sensor is below a
predetermined threshold value, a control mode is shifted into an
automatic steering mode. When an output of the torque sensor is
equal to or above the predetermined threshold value, the control
mode is shifted into the manual steering mode.
SUMMARY OF THE INVENTION
However, an automotive industry has demanded the following
requirements for the lane keeping assistance system.
That is to say, (1) Since a system cost becomes high with a
correction for a drift of an output value of the torque sensor
taken into consideration, the system cost is required to be
reduced, and (2) Since it is necessary to make a part of a steering
shift to which a steering torque is transmitted smaller in a
diameter (torsion bar), a torsional rigidity of a steering system
is reduced and a steering feeling thereof becomes worsened. Hence,
the vehicular steering system is required to maintain its torsional
rigidity and steering feeling thereof.
Therefore, it is, according to the requirements, difficult to mount
the torque sensor in the steering system in terms of the steering
performance and in terms of the cost. Then, in a case where such a
direct driver's steering intervention detecting device as described
above is not present, a steering angle sensor (having a steering
angular velocity output value) is used for a steering intervention
determination.
However, it is possible for the steering angle sensor to detect the
driver's steering intervention only if a certain steering angular
velocity occurs. Since the determination of the steering
intervention in which no steering angular velocity is developed
cannot be carried out, the determination of the steering
intervention cannot be made in a case where a steady-state steering
intervention (steering angular velocity .apprxeq.0.degree./S (zero
degree per second)) is carried out.
Since the steering operations by the vehicular driver and by the
steering control are interfered against each other, a large
driver's undesired feeling of the steering operation (a dull
steering and a sticky feeling) occurs.
It is noted that the steady-state steering intervention (steering
intervention without no generation of the steering angular
velocity) is one of the following cases.
1 A case wherein the driver is running on or near to a boundary of
the traffic lane (such lane markings as left and right white
lines). For example, in a case wherein a large-sized truck is
running on an adjacent traffic lane, the vehicle tends to run along
a line deviated toward another traffic lane opposite to the
adjacent traffic lane on which the truck is running. A case wherein
the vehicle is running on the traffic lane near to which a cobble
is present aside the traffic lane with a deviation thereof toward
the traffic lane side opposite to the cobble.
2 A case wherein the vehicle is not running along the white lines
but actually is running at a different side-road of the white
lines. For example, a case wherein, during a vehicular run on a
freeway, a guide-way or taxiway such as a guidance from a traffic
lane in the freeway to a service area is brought over. In addition,
the steering undesired feeling due to the steering interference is
that, in a case of the manual steering intervention, a controlled
output is caused to flow in a direction opposite to that caused by
the driver's intervention and undesired feelings of steering
wheel's weight increase and of a sticky feeling can be given to the
driver.
It is, hence, an object of the present invention to provide lane
keeping assistance system and method which can accurately determine
such a steady-state steering intervention without generation of the
steering intervention as described above and which can eliminate a
large undesired feeling of steering due to a steering
interference.
According to one aspect of the present invention, there is provided
a lane keeping assistance system for an automotive vehicle,
comprising: a traffic lane information detector (16) to detect an
information related to a traffic lane on which the vehicle is about
to run; a steering angle sensor (13) to detect a steering angle
(.theta.) of a steering wheel of the vehicle; a steering position
changing section (8, 9) by which the steering wheel of the vehicle
is enabled to be displaced independently of a manual steering
operation through the steering wheel; a controlled steering target
value setting section (15, FIG. 12) that sets a controlled steering
target value (.theta.*) when a controlled steering to follow the
traffic lane is carried out on the basis of at least the traffic
lane related information detected by the traffic lane information
detector and the steering angle detected by the steering angle
sensor; a controlled steering command value setting section (15,
FIG. 20) that outputs a control command value (Iout) in accordance
with the controlled steering target value; a control command value
filtering section (15, 22 of FIG. 2, and 62 through 66 of FIG. 6)
to filter the control command value to pass only frequency
components of the control command value lower than a predetermined
filter threshold value (fstr, fstr_low, fstr_mid, fstr_hi) to
derive a filtered control command value (Iout_lpf_th) during an
execution of the controlled steering; a manual steering
intervention detector (15, 23 of FIG. 2, 67 and 69 of FIG. 6) to
detect a steering intervention state to the controlled steering by
the manual steering operation when the filtered control command
value is in excess of a predetermined threshold control command
value (Iout_lpf_th); and a controlled steering target value limiter
(15, 24 and 25 of FIG. 2, and 70 and 71 of FIG. 6) to reduce the
control command value (Iout) toward zero value to suppress the
controlled steering target value toward a lower value direction
including zero when the manual steering intervention is detected by
the manual steering intervention detector.
According to another aspect of the present invention, there is
provided a method applicable to a lane keeping assistance system
for an automotive vehicle in which a control current is outputted
to a motor (8) of an automatic steering actuator coupled to a
vehicular steering system (3, 7) to provide a steering force
thereto to follow the vehicle along a traffic lane on a road
located in a vehicular forwarding direction during a vehicular run
in an automatic steering mode, the method comprising: detecting (20
of FIG. 2 and 60 of FIG. 9) the control current (Iout) to be
outputted to the motor during the automatic steering mode;
providing (22 of FIG. 2, 62 through 66 of FIG. 6) a filter for the
detected control current to pass only signal components of the
detected control current whose frequencies are lower than a
predetermined threshold frequency value of the filter to derive a
filtered control current; determining (23 of FIG. 2 and 67 and 69
of FIG. 9) whether a manual steering intervention to the automatic
steering occurs according to a magnitude of the filtered control
current, the manual steering intervention being determined to occur
depending on whether the magnitude of the filtered control current
is in excess of a predetermined threshold current value of the
filter; and reducing (24 and 25 of FIG. 2 and 70 and 71 of FIG. 6)
the control current outputted to the motor toward zero value when,
at the manual steering intervention determining step, the manual
steering intervention is determined to occur according to a result
of determination that the magnitude of the filtered control current
(Iout_lpf) is in excess of the predetermined threshold current
value (Iout_lpf_th).
This summary of the invention does not necessarily describe all
necessary features so that the invention may also be a
sub-combination of these described features.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a whole system configuration view of a vehicular
steering system to which a lane keeping assistance system for an
automotive vehicle in a first preferred embodiment according to the
present invention is applicable.
FIG. 1B is a rough configuration of an automatic steering
controller of the lane keeping assistance system in the first
embodiment shown in FIG. 1.
FIG. 2 is an operational flowchart executed by the automatic
steering controller shown in FIGS. 1A and 1B for a steering
intervention determination procedure.
FIG. 3 is a characteristic graph representing control current
distributions during the execution of the lane keep control and
during a driver's steering intervention.
FIG. 4 is a characteristic graph representing a gain characteristic
of a low-pass filter (LPF) used to detect a control current for the
driver's steering intervention.
FIG. 5 is a characteristic graph representing a steering
intervention determination region in a low-pass filter output
current-versus-frequency relationship.
FIG. 6 is an operational flowchart executed in automatic steering
controller and representing a flow of a steering intervention
determination procedure in a second preferred embodiment according
to the present invention.
FIG. 7 is a characteristic graph representing a control
current-versus-frequency at a low velocity region, a middle
velocity region, and a high velocity region.
FIG. 8 is a characteristic graph representing a cut-off frequency
characteristic of the low-pass filter with respect to a vehicular
velocity.
FIG. 9 is a characteristic graph representing the cut-off frequency
characteristic of the low-pass filter used to detect a driver's
steering intervention.
FIG. 10 is an explanatory view representing a vehicular position
with respect to a traffic lane during an input of an external
disturbance to the vehicle.
FIG. 11 is an explanatory view representing the vehicular position
with respect to the traffic lane during the input of the driver's
steering intervention.
FIG. 12 is an operational flowchart representing an example of a
main control routine on a lane keep control executed in the
automatic steering controller.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will hereinafter be made to the drawings in order to
facilitate a better understanding of the present invention.
First Embodiment
FIG. 1A shows a whole system configuration of a steering system of
an automotive vehicle to which a lane keeping assistance system in
a first preferred embodiment according to the present invention is
applicable.
In FIG. 1A, a column shaft 2 is inserted into an inside of a
steering column 1 and is supported by the steering column 1. A
steering wheel 3 is disposed on an upper end of column shaft 2. A
rack-and-pinion steering mechanism 6 is linked to steer left and
right road wheels 4 and 5 at a lower end of column shaft 2. An
assistance actuator 7 (or so-called, automatic steering actuator)
to provide an auxiliary steering torque is disposed at an
intermediate position of column shaft 2.
Assistance actuator 7 includes: an electric motor 8; an
electromagnetic clutch 9 disposed on a motor axle; a drive gear 10
rotationally driven by motor 8 via electromagnetic clutch 9; and a
worm-gear-to-speed-reduction mechanism having a driven gear 12
meshed with drive gear 10.
A steering angle sensor 13 to detect a rotational angle of column
shaft 2 is disposed on a position of column shaft 2 is disposed on
a position of column shaft 2 placed in proximity to steering wheel
3. An angle sensor 14 to detect a rotational angle of driven gear
10 is disposed. Sensor output signals from steering angle sensor 13
and angle sensor 14 are inputted to an automatic steering
controller 15.
Automatic steering controller 15 receives a video signal from a CCD
(Charge Coupled Device) camera 16 arranged to photograph a forward
road zone in a vehicular forwarding direction and a vehicular
velocity indicative signal from a vehicular velocity sensor 17 as
well as the sensor output signals from the steering angle sensor 13
and angle sensor 14.
In addition, automatic steering controller 15 outputs a control
current via a motor drive circuit 15g to motor 8 and outputs a
clutch or de-clutch command to electromagnetic clutch 9.
Furthermore, an automatic steering controller 15 implements an
image processing of road images in the vehicular forwarding
direction on the basis of the video signal form CCD camera 11,
extracts and discriminates boundary lines of a forward traffic lane
such as a white line (broken line form) or center (boundary) line
(solid line form), and generates a vehicular running state
information of a host vehicle (host vehicle means the vehicle on
which the lane keeping assistance system is mounted).
In addition, when an automatic steering mode is selected, both of a
steering torque and a target steering angle needed to follow the
host vehicle along the forward traffic lane are calculated. To make
the actual steering angle substantially equal to the target
steering angle, automatic steering controller 15 implements a
fundamental control of a lane keeping assistance by outputting the
control current to motor 8.
FIG. 1B shows a basic internal structure of automatic steering
controller 15.
Automatic steering controller 15 includes: a CPU (Central
Processing Unit, but also called Microprocessor unit) 15a; a V-RAM
(Video Random Access Memory) 15b; a RAM (Random Access Memory) 15c;
a ROM (Read Only Memory) 15d, an Input Port 15e, an Output Port
15f, motor drive circuit (PWM (Pulse Width Modulation) circuit)
15g, and a common bus.
Next, an operation of the above-described lane keeping assistance
system in the first preferred embodiment will be described.
[Steering Intervention Determination Procedure]
FIG. 2 is an operational flowchart representing a flow of a
steering intervention procedure executed by automatic steering
controller 15. Each step shown in FIG. 2 will be described
below.
At a step 20, controller 15 detects the control current outputted
to motor 8 from controller 15 (via the motor drive circuit
15g).
At the next step 21, controller 15 retrieves the vehicular velocity
from vehicular velocity sensor 17.
At the next step 22, controller 15 provides a low-pass filtering
process to pass signal components of only a low frequency range for
the detected control current at step 20 to calculate a filtered
output current Iout_lpf.
It is noted that although a cut-off frequency of the low-pass
filter is a predetermined constant value, another low-pass filter
having a cut-off frequency variable characteristic such that as the
vehicular velocity becomes higher the cut-off frequency is shifted
toward a higher direction may be used since the vehicular velocity
is retrieved at step 21.
At a step 23, controller 21 determines whether the calculated
filtered output current Iout_lpf is in excess of a steering
intervention threshold current Iout_lpf_th.
If No at step 23 (Iout_lpf .ltoreq.Iout_lpf_th), controller 15 does
not determine the steering intervention but returns to step 20. If
Yes at step 23 (Iout_lpf >Iout_lpf_th), controller 15 determines
that the steering intervention is present and the routine goes to a
step 24.
At step 24, controller 15 gradually reduces the output current to 0
[A]. It is noted that, basically, when the steering intervention is
determined to be present, the steering control may be turned to
off. However, since an abrupt (stepwise) change of a steering force
results in a steering unmatched feeling to a vehicular driver, the
output current is gradually reduced.
At the next step 25, controller 15 determines whether a time
duration from a time at which the answer of Yes is determined at
step 23 is elapsed by a set time duration t [seconds]. Until the
set time duration t is passed, the reduction process of the control
current at step 24 is continued. It is noted that a return
condition cannot be determined from the output current since the
output current is already reduced and a time management is used to
determine an automatic return.
[Steering Intervention Determination Action]
When the vehicle is running during an automatic steering mode, the
control current to make the host vehicle follow the traffic lane of
the vehicular forwarding road is outputted to motor 8 so that the
vehicular run to follow the traffic lane without the driver's
steering operation can be assured.
During the vehicular run in the automatic steering mode, controller
15 provides at step 22 in FIG. 2 the low-pass filtering process for
the control current outputted to the motor 8 to calculate the
filtered output current Iout_lpf. At step 23, if the filtered
output current Iout_lpf is in excess of steering intervention
output current threshold current Iout_lpf_th, controller 15
determines that the driver has intervened in the automatic steering
and the routine goes to step 24. At step 24, the control current
for motor 8 of assistance actuator 7 is gradually reduced.
That is to say, as viewed from a control current distribution
during the steering intervention in FIG. 3, the control current
distribution by a lane keep control indicates a high density in a
proximity to a vehicular yaw resonance of 1 Hz but that by a
steady-state steering intervention indicates a distribution at a
frequency region lower than that in the case of the lane keep
control since a steering velocity is extremely low in the
steady-state steering intervention. It is noted that since the
steering velocity occurs during the steering intervention at the
proximity to the frequency of the lane keep control, it is possible
to make the driver's intervention determination according to the
steering velocity (steering angular velocity).
Furthermore, during the steering intervention, since a large
control current against the driver's intervention is outputted from
controller 15, the output control current is constantly held at a
output current limier Ilmt like an adhesive so that the control
current distribution is concentrated in a control current limit
value region as denoted by oblique lines in FIG. 3.
Then, the low-pass filter (refer to FIG. 4) is used which has a
cut-off frequency fstr of a boundary frequency of two control
current distributions. When the low-pass filter (shown in FIG. 4)
processing is carried out for the control current to motor 8, a
frequency characteristic only according to the control current
(=filtered output current Iout_lpf) caused by the steering
intervention at the low frequency region as appreciated from FIG.
5.
Furthermore, if a region such that the filtered output current
Iout_lpf exceeds the steering intervention threshold current
Iut_lpf_th is prescribed, this region of steering intervention
determination corresponds to the control current limit value region
denoted by the oblique lines in FIG. 3. In other words, if the
filtered output current Iout_lpf is in excess of the steering
intervention threshold current Iout_lpf, controller 15 can
determine that the driver performs the steady-state steering
intervention.
Next, an advantage in the first embodiment will be described
below.
In the first embodiment, the control current is used to determine
the driver's steering intervention and, during the driver's
steering intervention determination, control mode is gradually
transferred to a manual steering mode by the vehicular driver.
Hence, although the driver's steering intervention determination is
based on the determination without use of the torque sensor to
directly detect the driver's steering intervention or without use
of the steering angle sensor to indirectly detect the driver's
steering intervention, the steady state steering intervention which
does not generate the steering angular velocity can accurately be
determined and such a large difference in the unmatched feeling of
steering due to a steering interference between the lane keep
control and the manual steering intervention by the driver can be
eliminated.
It is noted that in a case where the cut-off frequency of the
low-pass filter (LPF) is varied according to the vehicular
velocity, a more accurate determination of the steady-state
steering intervention can be carried out as will be described
later.
Second Embodiment
The whole configuration of the lane keeping assistance control is
the same as that in the first embodiment shown in FIGS. 1A and 1B.
Hence, the detailed explanation of the system configuration will
herein be omitted.
FIG. 6 shows an operational flowchart representing a flow of the
steering intervention determination procedure executed by automatic
steering controller 15 in the second preferred embodiment.
At a step 60 in FIG. 6, automatic steering controller 15 detects
the control current outputted to motor 8.
At a step 61, controller 15 retrieves the vehicular velocity.
At a step 62, controller 15 selects one of low-pass filters having
difference cut-off frequencies according to a magnitude of the
vehicular velocity retrieved at step 61. The magnitude of the
vehicular velocity is divided into three regions, i.e., a low
vehicular velocity region, a middle vehicular velocity region, and
a high vehicular velocity region.
At a step 63, controller 15 executes the low-pass filtering
procedure using the low vehicular velocity region low pass filter
having the cut-off frequency fstr_low for the detected control
current at step 60.
At a step 64, controller 15 executes the low-pass filtering
procedure using the middle vehicular velocity region low-pass
filter having the cut-off frequency frst_mid for the detected
control current at step 60.
While, at a step 65, controller 15 executes the low-pass filtering
procedure using the high vehicular velocity region low-pass filter
having the cut-off frequency frst_hi for the detected control
current at step 60.
At a step 66, the filtered control current Iout_lpf is calculated
from the low-pass filtered control current passed at any one of
steps 63, 64, and 65.
At a step 67, controller 15 determines if the filtered output
current Iout_lpf calculated at step 66 is in excess of the steering
intervention threshold current Iout_lpf_th. If No (Iout_lpf
.ltoreq.Iout_lpf_th) at step 67, controller 15 determine that there
is no steering intervention and the routine returns to step 60. If
Yes at step 67, the routine goes to a step 68.
At step 68, controller 15 retrieves a camera image and detects a
lateral deviation Ym of a vehicular running position from a center
position of the host vehicle running traffic lane.
At step 69, controller 15 determines if an absolute value
.vertline.Ym.vertline.of the lateral deviation detected at step 68
is in excess of an external disturbance determination deviation
threshold Ym_th. If No (.vertline.Ym.vertline..ltoreq.Ym_th) at
step 69, controller 15 determines that there is no steering
intervention and the routine returns to step 60. If Yes at step 68,
the routine goes to a step 70.
At step 70, controller 15 reduces gradually the output current
toward zero 0 [A]. It is noted that basically the control may be
turned off during the steering intervention. However, the abrupt
change results in the unmatched steering feeling and, therefore,
the output current is gradually reduced.
At the next step 71, controller 15 determines if the time duration
from the time at which the controller 15 determines Yes at step 69
has passed by the set time t [sec.]. Until the set time t, the
reduction process of the output current at step 70 is continued. It
is noted that the return condition is not determined from the
output current since the output current is already reduced but is
the automatic return according to the time management.
[Vehicular Velocity Dependent Change in Out-off Frequency]
An action to differ the cut-off frequency of the low-pass filter
according to the vehicular velocity will be explained below.
During the vehicular run in the automatic steering mode, controller
15 at step 62 selects one of the low-pass filters having mutually
different cut-off frequencies according to the magnitude of the
vehicular velocity (low vehicular velocity region, the middle
vehicular velocity region, and the high vehicular velocity region).
In other words, at the low vehicular velocity region, the low
vehicular velocity region low-pass filter having the cut-off
frequency fstr_low. At the middle vehicular velocity region, the
middle vehicular velocity region low-pass filter having the cut-off
frequency fstr_mid is selected. At the high vehicular velocity
region, the high vehicular velocity region low-pass filter having
the cut-off frequency frst_hi is selected. Then, the low-pass
filtering process is carried out for the detected control current
at any one of steps 63, 64, and 65 and at step 66 the filtered
output current Iout_lpf is calculated.
In details, as shown in FIG. 7, in the lane keep control, a control
response to follow the traffic lane is increased as a rise in the
vehicular velocity so that the control current distribution during
the lane keep control is shifted toward the higher frequency side.
In the same way, the control current distribution due to the
driver's steering intervention is also shifted toward the higher
frequency side as the vehicular velocity is increased. In other
words, suppose that the boundary frequency of the two control
current distribution during the driver's steering intervention and
the lane keep control is the cut-off frequency. As shown in FIG. 7,
the boundary frequency is varied in such a way as the cut-off
frequency fstr_low at the low vehicular velocity region, that
fstr_mid at the middle vehicular velocity region, and that fstr_hi
at the high vehicular velocity region.
For a switching method of the cut-off frequency according to the
vehicular velocity, it is desirable to vary continuously the
cut-off frequency according to the vehicular velocity as shown in
FIG. 8. However, in terms of processing capacity, such a method
that several low-pas filters having the different cut-off
frequencies are prepared and these filters are switched is general.
For example, in the case of the second embodiment, three cut-off
frequencies are switched as shown in FIG. 9.
Hence, since the cut-off frequency fstr of the low-pass filter is
varied according to the vehicular velocity, the more accurate
determination of the steady-state steering intervention can be
made.
[Steering Intervention Determination Action]
During the vehicular run in the automatic steering mode, if the
filtered output current Iout_lpf is in excess of the steering
intervention threshold current Iout_lpf_th at step 67 and the
detected lateral deviation absolute value .vertline.Ym.vertline.is
in excess of the set external disturbance determination threshold
Ym_th, controller 15 determines that the driver (driver' steering
operation) has intervened the automatic steering and the routine
shown in FIG. 6 goes to step 70 at which controller 15 reduces
gradually the control current for motor 8 of the assistance
actuator.
That is to say, as shown in FIG. 10, the control current is
supplied to motor 8 so that the host vehicle runs on a center part
of the traffic lane which indicates a target traffic lane in the
lane keep control against the input of an external disturbance such
as road surface cant, lateral wind, or so forth. On the other hand,
as shown in FIG. 11, the control current is supplied to motor 8 so
that the host vehicle is maintained to run on the traffic lane that
the vehicular driver intends in the same manner as the case of the
external disturbance, during the steering input by the driver.
Since this control current is adhered orheldon the limit value due
to the provision of the limiter in the output current, the
determination of whether it is the external disturbance input time
or the driver's steering input time cannot be made only by the
control current value.
However, during the external disturbance input, the host vehicle,
basically, runs on the center position of the traffic lane which is
the target traffic lane (refer to FIG. 10). While, during the
driver's steering input, the host vehicle runs on a position of the
traffic lane which is deviated from the center position of the
traffic lane toward one of the left and right white lines (lane
markers) in order to avoid collision against a large-sized truck
which is running on one of the adjacent traffic lanes or the
adjacent lane (refer to FIG. 11).
Therefore, it becomes possible to distinguish the driver's steering
input from the external disturbance input by determining the
driver's steering intervention using a logical AND condition
between the control current condition and the host vehicle position
deviation condition. Hence, a more accurate determination for the
steady-state steering intervention can be achieved.
It is noted that if a control current exceeding a control
limitation is caused to flow into motor 8 during the occurrence in
the external disturbance, the host vehicle runs deviating toward
one of the left and right white lines. However, in this state,
control is disabled and it is desirable to turn the control output
to OFF in the same way as the case of the driver's steering
intervention.
Other Embodiments
Although, in the lane keeping assistance system in each of the
first and second preferred embodiment, the low-pass filter (LPF) is
used to pass there through only the signal components in the low
frequency range to the control current, a band pass filter (BPF)
which passes the signal components of a middle frequency range
between the low frequency range lower than the lower cut-off
frequency and the high frequency range higher than the upper
cut-off frequency may be used.
Although, in the lane keeping assistance system in each of the
first and second embodiments, the present invention is applicable
to the controller from which the steering torque is provided for
the steering system during the automatic steering mode, the present
invention is also applicable to a controller from which a steering
reaction force torque is provided thereto. In the latter case, such
a control that as a magnitude of the intervention from the driver
becomes larger, the steering reaction torque becomes smaller is
carried out.
Lane keep Assistance Main Routine)
FIG. 12 shows an operational flowchart representing an example of
the lane keep control procedure executed by automatic steering
controller 15 in each embodiment during the automatic steering
mode.
FIG. 12 is a main interrupt routine executed whenever a
predetermined period of time, for example, 10 milliseconds has
passed.
At a step S1, controller 15 reads actual steering angle .theta.
detected by steering angle sensor 13, a vehicular velocity
detection value V detected by vehicular velocity sensor 17, a yaw
angle .PHI., lateral deviation y, and a radius of curvature .rho.
of the extracted white line detected from CCD camera 16 and image
processed by controller 15. Then, the routine goes to a step
S2.
At step S2, controller 15 calculates a target steering angle
.theta.* using the following equation (1) on the basis of the yaw
angle .PHI., the vehicular lateral deviation y, and the radius of
curvature .rho..
In the equation (1), Ka, Kb, and Kc denote preset control gains
varied according to the vehicular velocity and target steering
angle .theta.* indicates a positive value when the steering
direction is in a clockwise direction as viewed from the driver's
position and a negative value when the steering direction is in a
counter-clockwise direction as viewed from the driver's
position.
Next, at a step S3, automatic steering controller 15 calculates the
motor supply current Iout using the following equation (2) and
performs a PID (Proportional-Integration-Differential) control to
make the actual steering angle .theta. substantially equal to
target steering angle .theta.*. Then, the motor supply current,
i.e., the output current from controller 15 to motor 8 is stored
into a motor supply current memory location to update the
corresponding contents of the motor supply current memory
location.
In the equation (2), Kvi denotes a control gain to convert a
voltage value into a current value, Kp denotes a proportional gain,
Ki denotes an integration gain, and Kd denotes a differential
gain.
It is noted that a reason for controller 15 to calculate the motor
supply current Iout using the above-described equation (2) is that
controller 15 subtracts actual steering angle .theta. to derive a
deviation .DELTA..theta. from both steering angle values, performs
the PID calculation for the deviation .DELTA..theta. to derive a
target motor control voltage V*, and converts target motor control
voltage V* into the corresponding current value by a multiplication
of the target motor control voltage V* by control gain Kvi to
calculate the motor supply current Iout to motor 8, and the series
of these calculations are carried out in a feedback loop
configuration of controller 15 itself, motor 8, and associated
sensors 13, 14, 16, and 17, and, in this feedback loop
configuration, controller 15 performs its equivalent
calculations.
At the next step S4, automatic steering controller 15 determines
whether the calculated motor supply current Iout is in excess of
the current limit value Ilimit stored in a current limit value
memory location. If Iout .ltoreq.Ilimit at step S4, the routine
goes to a step S6. If Iout >Ilimit at step S4, the routine goes
to a step S5.
At step S5, automatic steering controller 15 assigns the current
limit value Ilimit (Ilimit.fwdarw.Iout) and stores this motor
supply current Iout (,i.e., Ilimit) into the motor supply current
memory location to update the corresponding contents and the
routine goes to step S6.
At step S6, controller 15 outputs the motor supply current (control
current) Iout stored in the motor supply current memory location
which is pulse-width modulated in PWM (Pulse-Width Modulator)
circuit 15g to motor 8 whose direction is in accordance with the
present steering direction.
Traffic lane information detecting means corresponds to CCD camera
16 and automatic steering controller 15. Steering angle detecting
means corresponds to steering angle sensor 13 and is exemplified by
a U.S. Pat. No. 6,155,106 issued on Dec. 5, 2000. The CCD camera is
exemplified by a U.S. Pat. No. 6,226,592 issued on May 1, 2001. A
controlled steering target value corresponds to target steering
angle .theta.* described above. A control command value corresponds
to the control current Iout (this corresponds to the motor supply
current). It is also noted that angle sensor 14 shown in FIG. 1A is
used to detect the rotational angle of drive gear 10 to confirm the
present steered position of the vehicle, electromagnetic clutch 9
is in the clutched state in response to the clutch command from
automatic steering controller 15 during the automatic steering
mode, and the automatic steering corresponds to a controlled
steering.
The entire contents of a Japanese Patent Application No.
2000-268218 (filed in Japan on Sep. 5, 2000) are herein
incorporated by reference. Although the invention has been
described above by reference to certain embodiment of the
invention, the invention is not limited to the embodiments
described above. Modifications and variations of the embodiments
described above will occur to those skilled in the art in the light
of the above teachings. The scope of the invention is defined with
reference to the following claims.
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